Can C 0x Enhance the Reusability of the Key-Oriented Access-Protection Pattern?

Can We Improve the Reusability of the Key-Oriented Access-Protection Pattern?

The key-oriented access-protection pattern utilizes a key class to control access to specific methods. However, it can be cumbersome to repeat passkey creation for different classes and methods. This question explores possible enhancements to increase its reusability.

In C 0x, two advancements address this issue:

1. Variadic Templates: Templates can now accept a variable number of arguments, allowing functions to be specified with passkeys in a more flexible manner.
2. Friend Template Parameters: Template parameters can be declared as friends, eliminating the need to explicitly define friend classes for each key-oriented method.

Utilizing these capabilities, the updated code is greatly simplified:

template <typename Key>
class passkey
{
private:
    friend Key;
    passkey() {}
};

template <typename... Keys>
class allow
{
public:
    template <typename Key>
    allow(const passkey<Key>&amp;)
    {
        static_assert(is_contained<Key, Keys>::value, "Passkey is not allowed.");
    }
};

This updated version provides several benefits:

• Generic Code: The boilerplate code handles all the complexity, relieving users from defining specific passkey classes.
• Caller Simplicity: Users only need to create passkeys relevant to their specific requirements.
• Reduced Drawbacks: The previous drawbacks of requiring specific passkey creation and macro definition are eliminated.

With these enhancements, the key-oriented access-protection pattern becomes more expressive and reusable, greatly simplifying the process of implementing access control in complex software systems.

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